1. Field of the Invention
The present invention relates to pneumatic tires and more particularly to studded tires wherein a plurality of anti-skidding spikes are struck into a tread surface of the tire.
2. Prior Art
As is well-known, spikes for tires are of tubular type and pin type, which are distinguished in accordance with the shape of a chip provided on a shank and consisting mostly of super hard alloy as follows: the former type is hollow tubular and the latter type is non-hollow cylindrical.
The performances of both spikes as described above were compared by mounting tires having a size 6.00-13-6PR on a vehicle having a gross vehicle weight of 1,200 Kg and testing them on frozen road to obtain results as shown in the following Table 1.
Table 1 ______________________________________ Stopping distance Tractive force (m) (Kg) ______________________________________ at static at 30 Km/h 40 Km/h state spinning ______________________________________ Tubular 9.9 16.6 263 105 type Pin type 13.0 26.9 210 80 ______________________________________
As seen from Table 1, the tubular type spike is generally superior in performance to the pin type spike. This is due to the difference of edge length scratching the frozen surface between the spikes.
However, studded tires do not necessarily run only on a frozen road, but frequently run on non-frozen and non-snowed roads. In the latter case, the road surface is damaged by the spikes in the tire.
Of course, this degree of damage is more severe in the use of tubular type spike having improved performances on a frozen road than the use of pin type spike. Therefore, some western countries prohibit the use of spikes for tires.
Furthermore, in high-speed running (the running speed on paved road is as high as 80 to 110 Km/h although the speed on snowed and frozen roads is at most 30 to 40 Km/h), the tubular type spike is apt to cause tottering thereof prior to generation of heat and falling off of these spikes as compared with the pin type spikes is greater. Accordingly, the use of pin type spikes is particularly useful for all-weather type tires requiring high-speed durability and high-speed safety.